IPs for SMTP connection whitelisting - Google SMTP rejecting IO SMTP connections

Awesome - Is there a way to bypass the InflatableOffice request for a username/password?

I've configured our SMTP relay to work off whitelisted IPs for any address in our domain without requiring authentication, but I'm unable to send a test message from InflatableOffice without including a password.

Edit: To clarify - Previously, I would use SMTP authentication and I would use an "App Password" but Google depreciated those and now requires OAuth. So my only option for SMTP relay is via IP whitelisting and not SMTP authentication.

I'm fairly certain google still supports app passwords. You'd need to have 2-step verification on though. you'd have to reach out to google for more info.

https://support.google.com/accounts/answer/185833?hl=en

That was the issue, I just got off a support call with Google over the same thing. They discontinued "Less secure apps" but App Passwords are still fine with 2SV.

I thought we had 2SV enabled on the main account because it prompts for a code, but it's technically disabled. Fixing that now and we should be good.

I'll still whitelist the IPs in addition just for the extra security. Thanks for the assistance, that's what I get for assuming and not verifying.

Note: Test results are at the end, this appears to be an issue where Google rejects Inflatable Office SMTP connections.

For now, I've had to switch to sending via Gmail Authentication, which means I have to limit outbound email to avoid Google's limits.

Using an App password, smtp-relay.gmail.com is still rejecting all connections from Inflatable Office with the following error:

smtp-relay.gmail.com:587 [SMTP: HELO was not accepted (code: -1, response: )]

I've tried the following:

Allowed Senders:

* Only registered Apps users in my domain

* Only addresses in my domains

Authentication:

* Only accept mail from the specified IP addresses: 208.92.218.149, 209.250.2.66

* Require SMTP Authentication

* Both (Specific IP + SMTP Authentication)

Encryption:

With and without TLS enforcement

Ports: 25 and 587 (With and without TLS)

All attempts were using the App Password.

Additionally, I've tested the App Password via gmass.co/smtp-test, and it works fine. Results below:

Connected to smtp://smtp-relay.gmail.com:25/?starttls=when-available
<< 220 smtp-relay.gmail.com ESMTP d75a77b69052e-47ae9c16c43sm1118111cf.6 - gsmtp
>> EHLO [172.31.11.248]
<< 250-smtp-relay.gmail.com at your service, [54.212.131.181]
<< 250-SIZE 157286400
<< 250-8BITMIME
<< 250-STARTTLS
<< 250-ENHANCEDSTATUSCODES
<< 250-PIPELINING
<< 250-CHUNKING
<< 250 SMTPUTF8
>> STARTTLS
<< 220 2.0.0 Ready to start TLS
>> EHLO [172.31.11.248]
<< 250-smtp-relay.gmail.com at your service, [54.212.131.181]
<< 250-SIZE 157286400
<< 250-8BITMIME
<< 250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH
<< 250-ENHANCEDSTATUSCODES
<< 250-PIPELINING
<< 250-CHUNKING
<< 250 SMTPUTF8
>> AUTH PLAIN AG5pY2suc2VhcnNAYm91bmNlcnMtci11cy5jb20AYWJoc2ZmZmZta3FpZG14aA==
<< 235 2.7.0 Accepted
>> MAIL FROM:<nick.sears@bouncers-r-us.com> SIZE=578
>> RCPT TO:<michael.k.purdue@gmail.com>
<< 250 2.1.0 OK d75a77b69052e-47ae9c16c43sm1118111cf.6 - gsmtp
<< 250 2.1.5 OK d75a77b69052e-47ae9c16c43sm1118111cf.6 - gsmtp
>> DATA
<< 354 Go ahead d75a77b69052e-47ae9c16c43sm1118111cf.6 - gsmtp
>> From: nick.sears@bouncers-r-us.com
>> Date: Mon, 21 Apr 2025 20:34:00 퍍
>> Subject: SMTP test from smtp-relay.gmail.com
>> Message-Id: <ULNFVWJRYPU4.ETT3P7JPCCBC1@WIN-AUIR3RRGP88>
>> To: michael.k.purdue@gmail.com
>> MIME-Version: 1.0
>> Content-Type: multipart/alternative; boundary="=-OvjFzLtb47vrxN7A4IyLqg=="
>>
>> --=-OvjFzLtb47vrxN7A4IyLqg==
>> Content-Type: text/plain; charset=utf-8
>>
>> Test message
>> --=-OvjFzLtb47vrxN7A4IyLqg==
>> Content-Type: text/html; charset=utf-8
>> Content-Id: <ULNFVWJRYPU4.1D44OMTIQ5IH3@WIN-AUIR3RRGP88>
>>
>> <b>Test message</b>
>> --=-OvjFzLtb47vrxN7A4IyLqg==--
>> .
<< 250 2.0.0 OK 1745267642 d75a77b69052e-47ae9c16c43sm1118111cf.6 - gsmtp